The main challenge faced in satellite-based quantum communications is the degradation of the signal as it is transmitted through the turbulent atmosphere of Earth [1]}, [2]}, [3]}, a degradation that is almost always larger than the noise introduced by the components used [4]}.
It is well documented that uplink satellite laser communications is considerably more challenging compared to downlink satellite transmission: the turbulent eddies in the Earth's atmosphere have a more disruptive effect in the uplink channel. This is because the size of the eddies
encountered by a laser beam in the downlink at the atmospheric entry point
are significantly larger than the laser beam's transverse dimensions (spot size) at the entry point, whereas in the uplink the opposite is true [5]}. The consequence of this is that an asymmetry in the channels exists, with the uplink beam profile evolving in a more random fashion, especially in regard to beam wandering effects. Ultimately, this asymmetry manifests itself in higher losses in the uplink channel [5]}, [7]}.
